Annular saws have long been known but have not until recently been used to any great extent. The reason for this is that the driving of the saw blades has created a problem which has been difficult to solve. For the rotation of saw blades in annular saws, either a gear-wheel drive or a friction drive is used. Gear-wheel drive systems are described, for example, in the U.S. Pat. Nos. 2,804,105, 2,972,363, 3,373,489, and 3,808,685. The major advantage of the gear-wheel drive is that it does not give rise to considerable losses of energy due to friction, so that the drive power of the saw may be used more efficiently for the sawing work. A notable disadvantage, however, is that the wear between the gear-wheel and the annular saw blade is very great, particularly when sawing concrete, metal and other heavy wear materials, since it is impossible to prevent saw dust from getting between the gear-wheel and the saw blade. Due to the wear, the saw blade is gradually displaced in the radial direction. As a result, the gear pitch of the saw blade changes so that it does not match the pitch of the driving gear-wheel. This tendency after a comparatively short period of time will cause a sudden disintegration of the saw blade. This is a problem not only as far as cost is concerned but also because it means that the risk of accidents is significantly increased.
Friction-based transmissions for annular saw blades are described, for example, in the U.S. Pat. Nos. 3,221,783, 3,438,410, 3,930,310, and Re-27,716. Typically, these systems use one or more drive wheels which bear against one side of the web of the saw blade with opposite support from an opposing wheel bearing against the other side of the saw blade. In order to obtain sufficiently good friction between the drive wheel and the saw blade, it generally necessary to apply a high pressure between the drive wheel and the saw blade. As a result, heat is generated to such a high degree that the blade may be deformed, which can cause sudden disintegration of the blade. Moreover, the bearings of the drive wheels may be damaged by the high pressure. In order to improve the friction and hence the driving it has been suggested to deposit a wear layer on the drive wheel. This, however, has not solved the problem. The inventions described in U.S. Pat. Nos. 4,472,880 and 4,793,065 constituted major achievements within this technical field and brought about a significant break through for the annular saw. According to these inventions, which are based on the principle of friction drive, the driving force is applied to the inner rim portion of the annular saw blade which is designed as a wedge. Although these inventions were major technical achievements they do not however provide a solution to the driving problem which is free of disadvantages. For example, much poser is lost because of high pressure and great friction between the drive wheel and the saw blade.
Another problem which concerns all types of annular saws is that they give rise to an uncomfortably high noise level. While a conventional circular saw blade is kept firmly clamped on a driving shaft, an annular saw is rotated between one or more drive rollers and a plurality of support rollers. All these rollers together generate rattle and vibrations which cause a higher noise level than is experienced with conventional circular saws.